Re: Am I an 'operator' at anchor?
I am not a lawyer, but in CA, at least for road vehicles, a DUI requires (among other things) that the operator both cause the vehicle to move, and that the vehicle does move. They always say 'however slightly' although I don't know if this is statutory or jurisprudence. The boat definitely moves at anchor, but it seems most likely that the operator (if there is one) is not actually causing the boat to move, from a legal standpoint.
As a practical matter, the state law always seems interested in who is at the wheel or tiller, and my understanding is that no one else matters in the slightest, even if they say they're the "captain" or anything similar.
On the other hand, I've heard stories of crappy cops who give people a hard time about stuff even though it's probably not actually illegal. So the best thing might be to just ask cops in the relevant jurisdiction (by anonymous telephone call) whether they would have a problem with this.